The engineering behind ceramic space heaters is pretty simple. There is a ceramic element that conducts heat very well, and air is blown over this element by a fan and then delivered to the room.
Generally speaking these units do not put out enormous amounts of heat like propane space heaters might do, but in many situations they put out more than enough. If you do not suffer with very cold winters and you have done some basic home insulation, then it is quite possible that something like a ceramic heater can boost the heat in just the right area of the house.
The main benefits of a ceramic ceramic space heater is that it is small and lightweight - highly portable! They also have a safety advantage over many other portable space heaters in that the ceramic does not get so hot that it presents a fire risk. Any metal parts of the unit will get hot, and you should still follow all the basic safety rules like not putting the heater right by your drapes etc, but fundamentally these are safe heaters.
Like all electrical units, you can say these are energy efficient space heaters in that close to 100% of the electricity they consume goes to heating your space. Do not forget that the electricity is often produced in a less than efficient way however, and it is probably not environmentally friendly to heat a whole house with ceramic units in every room.